In lithographic printing, it is desirable to have a thin layer of wetting liquid applied to the plate cylinder to enhance the application of ink and to better define the printing and non-printing areas of the printing plate. See U.S. Pat. Nos. 3,701,316 and 4,290,260, for example.
Existing devices which perform the dampening function normally utilize a system of rolls wherein a dampening roll provides a layer of liquid to be distributed by surface contact to a plurality of rolls in the system as the dampening roll is exposed to a reservoir of fluid. The system is shut down in times of non-printing. When the system is started again, substantial time is taken to obtain the proper ink and water balance on the rolls as the fountain roll again starts to move fluid from the reservoir over the surfaces of the rolls to the printing plate. As the system starts up, substantial amounts of paper are wasted until the ink-fluid balance is obtained.
It is therefore a principal object of this invention to provide a dampening system for printing machines wherein the fountain roll runs continuously in operative contact with the fluid reservoir, but where its surface contact with downstream rollers is interrupted when the printing system is discontinued.
A further object of this invention is to provide a dampening system for printing machines wherein the water accumulating on the surface of the fountain roll will go back into the fluid reservoir when the system is not printing and when it is not desirable to distribute fluid to the rolls of the system.
These and other objects will be apparent to those skilled in the art.
A fluid dampening system for a printing machine has a frame and a printing roll on the frame for holding a circular printing plate. A fluid reservoir is on the frame and a fountain roll is on the frame and is partially immersed in the fluid reservoir. A second roll is on the frame and is normally in surface contact with the fountain roll. A third roll is on the frame and is normally in surface contact with the fountain roll. A plurality of additional rolls are on the frame sequentially in surface contact with each other and with the third roll and the printing roll so that when all of the aforesaid rolls are rotated and in surface contact with each other, fluid will be transferred from the surface of the fountain roll to the surface of the third roll and sequentially on the surface of the additional rolls to the surface of the printing roll.
A drive system on the frame connects the second roll and the third roll whereby the third roll drives the second roll which in turn drives the fountain roll. A linkage system is provided for breaking the fountain roll away from surface contact with the third roll while all the rolls are rotating to separate the fountain roll from surface contact with the third roll to prevent fluid from moving from a surface of the fountain roll to the third roll and to the rolls downstream from the third roll, while still permitting all the rolls to be simultaneously rotated.